Coated abrasive articles are normally prepared by coating at least one surface of a substrate with a first adhesive binder layer, often referred to as the "make" coating. Particles of abrasive material are applied to the coated substrate and partially embedded therein. A layer of a second binder, often referred to as the "size" coating, is then applied over the abrasive particles and make coating. Typical abrasive coatings generally include a make coating, abrasive particles, and a size coating. Anti-loading materials have also been included in a further optional layer, referred to as a "super-size" coating, which prevents buildup on the abrasive surface and, therefore, increases the useful life of the article.
Resilient or conformable abrasive articles, such as sanding sponges, are known in the prior art. Such abrasive articles have been found useful in cleaning, polishing, abrading, and dimensioning materials such as wood, metal, plastic, and the like, especially when such materials have and are to retain irregular, relieved, or otherwise intricate surface contours, or, when the manual control of working pressures between the abrasive article and the workpiece is desirable, such as when smoothing interior drywall surfaces.
To maintain the resilient properties of the abrasive article, flexible elastomeric binders are often used to adhesively bond the abrasive particles to a major surface of the foam substrate. In addition to using elastomeric binders, most conventional resilient abrasive articles are constructed so that each coating layer is at least as flexible as the underlying coating layer. Thus, for a typical resilient abrasive article having a make coat applied to a resilient foam substrate, abrasive particles embedded in the make coat, and a size coat applied over the make coat and abrasive particles, the size coat would be at least as flexible as the make coat. Such a configuration allows the abrasive article to maintain its flexibility and prevents the abrasive coating from cracking or splitting as the abrasive article is run over sharp corners or edges of a work surface during use. Flexible make and size coats, however, are soft and therefore do not provide adequate lateral support for the abrasive particles. As a result, the particles tend to tilt relative to the foam substrate as the abrasive article is pressed and moved along the work surface, thereby greatly reducing the effectiveness of the abrasive article. In addition, the soft size coat tends to rapidly buildup with swarf which shortens the useful life of the abrasive article.
Hard or rigid size coats are desirable because they provide lateral support for the abrasive particles which increases cut, and because they reduce buildup which increases the life of the article. However, when hard, non-elastomeric binders such as phenol-formaldehyde condensates are coated onto foam substrates, the resilient qualities of the foam substrates are quickly overcome by the physical properties of these binders, rendering the resultant abrasive article brittle and susceptible to cracking, tearing, and puncturing under normal use. The cracking and tearing of the abrasive article produces an inconsistent finish on the work surface and leads to premature failure of the abrasive article. To avoid the problems associated with hard size coats, most commercially available resilient abrasive articles either have been formed without a size coat or have been formed with a size coat that is at least as flexible as the make coat.
The Ruid et al. U.S. Pat. No. 4,629,473 discloses a resilient abrasive polishing product including a primary backing, a resilient layer laminated to the primary backing, and abrasive particles embedded in an elastomeric make coat on the side of the resilient layer opposite the primary backing. The product can also include an intermediate coating between the resilient layer and the elastomeric make coat, and a phenolic resin sizing adhesive layer. The primary backing can be formed of a finished cloth, paper, vulcanized fiber, non-woven webs, or plastic film. These materials are relatively inelastic and therefore prevent the resilient layer, elastomeric make coat, and size coat from stretching or elongating. This, in turn, prevents the size coat from cracking and resilient layer from tearing. The backing, however, significantly adds to the overall cost of the product. In addition, the resilient layer is formed of a thin reticulated foam layer having a thickness of 1.44 to 2.41 millimeters. Having a thin resilient layer further adds to the inflexibility of the product and makes it unsuitable for many finishing applications.
It would therefore be desirable to provide a resilient abrasive article having a resilient elongatable foam substrate thick enough to conform to a contoured surface, abrasive particles adhesively bonded to the substrate with a flexible make coat, and a hard, relatively inflexible, size coat applied over the abrasive particles and flexible make coat. More specifically, it would be desirable to provide a resilient abrasive article having a hard size coat to provide lateral support for the abrasive particles and resist swarf buildup, but which does not suffer from the cracking problem associated with conventional resilient abrasive articles having a hard size coat. It would also be desirable to provide such a resilient abrasive article which does not require an inelastic backing to prevent such cracking.